Changes

'''Metallicity''' is a term in [[astronomy]] that refers to the proportion of elements in an astronomical object (usually a [[star]]) that are other than [[hydrogen]] or [[helium]].  In astronomy, all elements heavier then hydrogen and helium are collectively referred to with the blanket term "metals".<ref name="metal">https://edocs.uis.edu/jmart5/www/rrlyrae/metals.htm</ref>  Therefore a star or a [[nebula]] that contained significant amounts of elements such as [[carbon]], [[oxygen]], or [[nitrogen]] would be considered "metal rich" even though those same elements are classified as nonmetals in chemistry.<ref>http://www.wisegeek.com/what-is-metallicity.htm</ref>

'''Metallicity''' is a term in [[astronomy]] that refers to the proportion of elements in an astronomical object (usually a [[star]]) that are other than [[hydrogen]] or [[helium]].  In astronomy, all elements heavier then hydrogen and helium are collectively referred to with the blanket term "metals".<ref name="metal">https://edocs.uis.edu/jmart5/www/rrlyrae/metals.htm</ref>  Therefore, a star or a [[nebula]] that contained significant amounts of elements such as [[carbon]], [[oxygen]], or [[nitrogen]] would be considered "metal rich" even though those same elements are classified as nonmetals in chemistry.<ref>http://www.wisegeek.com/what-is-metallicity.htm</ref>

Usually, metallicity is expressed in terms of the relative amounts of [[iron]] and hydrogen present in a star, since iron is among the easiest elements to measure with spectral data in the visible spectrum.  This is determined by analyzing absorption lines in a stellar spectrum using a spectrometer, compared to the star's solar value.  The ratio of the amount of iron to the amount of hydrogen in the object is divided by the ratio of the amount of iron to the amount of hydrogen in the Sun (which has a metallicity of 1.6 percent by mass). This value, expressed as [Fe/H], is calculated using the following logarithmic formula.<ref name="metal"/>

Usually, metallicity is expressed in terms of the relative amounts of [[iron]] and hydrogen present in a star, since iron is among the easiest elements to measure with spectral data in the visible spectrum.  This is determined by analyzing absorption lines in a stellar spectrum using a spectrometer, compared to the star's solar value.  The ratio of the amount of iron to the amount of hydrogen in the object is divided by the ratio of the amount of iron to the amount of hydrogen in the Sun (which has a metallicity of 1.6 percent by mass). This value, expressed as [Fe/H], is calculated using the following logarithmic formula.<ref name="metal"/>